From 5bd40baed29e82c7772e1a895663d942e04d6611 Mon Sep 17 00:00:00 2001
From: Karl Tauber <karl@jformdesigner.com>
Date: Tue, 12 May 2020 23:26:52 +0200
Subject: [PATCH] Extras: TriStateCheckBox: paint magenta rectangle when used
 in LaFs that do not support third state

---
 .../flatlaf/extras/TriStateCheckBox.java      | 27 ++++++++++++++++---
 1 file changed, 24 insertions(+), 3 deletions(-)

diff --git a/flatlaf-extras/src/main/java/com/formdev/flatlaf/extras/TriStateCheckBox.java b/flatlaf-extras/src/main/java/com/formdev/flatlaf/extras/TriStateCheckBox.java
index 4c13396b..dd4871e9 100644
--- a/flatlaf-extras/src/main/java/com/formdev/flatlaf/extras/TriStateCheckBox.java
+++ b/flatlaf-extras/src/main/java/com/formdev/flatlaf/extras/TriStateCheckBox.java
@@ -16,17 +16,23 @@
 
 package com.formdev.flatlaf.extras;
 
+import java.awt.Color;
+import java.awt.Graphics;
 import java.awt.event.ItemEvent;
 import javax.swing.JCheckBox;
+import javax.swing.LookAndFeel;
+import javax.swing.UIManager;
+import com.formdev.flatlaf.FlatLaf;
 
 /**
  * A tri-state check box.
- *
+ * <p>
  * To display the third state, this component requires an LaF that supports painting
  * the indeterminate state if client property {@code "JButton.selectedState"} has the
  * value {@code "indeterminate"}.
- *
+ * <p>
  * FlatLaf and Mac Aqua LaF support the third state.
+ * For other LaFs a magenta rectangle is painted around the component.
  *
  * @author Karl Tauber
  */
@@ -58,7 +64,7 @@ public class TriStateCheckBox
 			@Override
 			public void setSelected( boolean b ) {
 				switch( state ) {
-					case INDETERMINATE:			setState( State.SELECTED ); break;
+					case INDETERMINATE:	setState( State.SELECTED ); break;
 					case SELECTED:		setState( State.UNSELECTED ); break;
 					case UNSELECTED:	setState( thirdStateEnabled ? State.INDETERMINATE : State.SELECTED ); break;
 				}
@@ -104,4 +110,19 @@ public class TriStateCheckBox
 	public void setSelected( boolean b ) {
 		setState( b ? State.SELECTED : State.UNSELECTED );
 	}
+
+	@Override
+	protected void paintComponent( Graphics g ) {
+		super.paintComponent( g );
+
+		if( !isThirdStateSupported() ) {
+			g.setColor( Color.magenta );
+			g.drawRect( 0, 0, getWidth() - 1, getHeight() - 1 );
+		}
+	}
+
+	private boolean isThirdStateSupported() {
+		LookAndFeel laf = UIManager.getLookAndFeel();
+		return laf instanceof FlatLaf || laf.getClass().getName().equals( "com.apple.laf.AquaLookAndFeel" );
+	}
 }